1. Field of the Invention
The present invention relates to an information recording/reproducing apparatus for recording and reproducing information by irradiating a light beam from a laser, and in particular to an information recording/reproducing apparatus having a laser driver capable of generating a recording current signal corresponding to a binary signal by obtaining the binary signal, such as an NRZ (Nonreturn-to-Zero) signal, and a clock signal in synchronism therewith.
2. Description of the Related Art
An optical information recording/reproducing apparatus, wherein recording marks, such as hole pits, phase-change pits, pigment pits, magnetized domains, and so on, are formed on a recording film of a recording medium for recording information, and the information is reproduced by use of a reflection light from the recording medium, since a plurality of information recording mediums (hereinafter referred to as an xe2x80x9coptical discxe2x80x9d) can be used in an exchangeable manner, has a characteristic that a large amount of information can be recorded therein and reproduced therefrom, and therefore it is widely used as a large capacity external memory device for use with, for example, a personal computer and a large-sized computer.
In recent years, accompanying an increase in recording density thereof, it is required that the marks (or the pits) to be recorded on the surface of the information recording medium must be formed to be equal to or less than 0.5 xcexcm in diameter, for example, and for achieving such forming of the marks, recording power must be divided by a timer pulse period (i.e., multi-pulsated), and further there is needed a power control for altering or changing the level thereof at various values (for example, 3 values or 4 values). Also, for optimizing the time distances between a group of the recording marks and a group of spaces located therebetween, there is needed an adaptive control for variably controlling the time positions and the pulse widths of the recording pulses which are divided depending upon adjacent space lengths and mark lengths (hereinafter this control is referred to as a xe2x80x9crecording strategy controlxe2x80x9d) when recording the marks.
For conducting such a recording strategy control, a rise-time (Tr)-fall-time (Tf) characteristic of each pulse of the above-mentioned multi-pulses must be taken into consideration. In this instance, a time period of approximately several nanoseconds is needed for the Tr-Tf characteristic, and further for making the Tr-Tf characteristic operable at high speed corresponding to an increase in the disc rotational speed upon a requirement of high speed transfer recording. However, it is very difficult to transfer the recording pulses up to the laser mounted on an optical head without deterioration in the Tr-Tf characteristic of the waveforms thereof. In the construction of the prior art, in particular a circuit for executing the recording strategy control is disposed on a substrate at a side of modulation circuits, and therefore the transmission length for the recording pulse waveforms from the substrate up to the optical head needs to be long in the construction thereof.
An object of the present invention, for solving the problems mentioned above, is to provide an information recording/reproducing apparatus with which high density recording and high speed transfer recording can be performed.
Further, another object of the present invention is to provide an information recording/reproducing apparatus providing improved reliability in recording and reproducing operations of the information data into and from the information recording medium by use of a laser driver having a circuit for executing the recording strategy control on various recording mediums.
An outline of the present invention for achieving the above objects is as follows.
A laser driver capable of performing recording strategy control is disposed adjacent to a semiconductor laser element so as to reduce deterioration of the Tr-Tf characteristic in the drive current waveforms therefrom.
The laser driver can generate a recording current signal corresponding to a binary signal by obtaining the binary signal, such as an NRZ modulation signal from a modulation circuit, and a clock signal being synchronized therewith, and by making a PLL circuit disposed therein to oscillate at a recording frequency. However, when an oscillation condition of the PLL circuit becomes abnormal, a standard recording frequency also becomes abnormal, and therefore it is impossible to perform a normal recording operation. Accordingly, within the laser driver, there is provided a PLL unlock detection circuit for detecting the oscillation condition of the PLL circuit, and transmitting a detection signal from the unlock detection circuit to a calculation/control circuit for controlling the recording/reproducing operations so as to control the recording operation.
Here, assuming a case where the information data is recorded onto a CD-R disc, there is a necessity to sample-hold a DC level corresponding to a reproducing power level among pulse modulated reflection lights for the purpose of detecting a servo signal or the like when recording the CD-R. For this, a delay circuit is provided for the purpose of bringing the NRZ modulation signal from the modulation circuit into line with the reflection light in timing thereof. In this instance, there occurs a problem that a cost increases due to the provision of the delay circuit in addition to the modulation circuit.
Accordingly, upon the basis of the construction according to the present invention mentioned above in which the binary signal and the clock signal being synchronized therewith are obtained so that a recording current signal can be generated corresponding to the binary signal through the delay circuit disposed therein, an output of the delay circuit is transmitted as a monitor signal to the calculation/control circuit for managing the recording/reproducing operations, thereby generating a timing signal for conducting the sample-hold of the reflection light from the recording medium based upon the monitor signal.